Instrumented prosthetic foot

ABSTRACT

The present invention discloses an instrumented prosthetic foot for use with an actuated leg prosthesis controlled by a controller, the instrumented prosthetic foot comprising a connector to connect the instrumented prosthetic foot to the leg prosthesis, an ankle structure connected to the connector, a ground engaging member connected to the ankle, at least one sensor for detecting changes in weight distribution along the foot, and an interface for transmitting signals from the sensor to the controller.

TECHNICAL FIELD

The present invention relates to a prosthetic foot for use with acontrol system and/or a method for controlling an actuated legprosthesis.

BACKGROUND

As is well known to control engineers, the automation of complexmechanical systems is not something easy to achieve. Among such systems,conventional powered artificial limbs are notorious for having controlproblems. These conventional prostheses are equipped with basiccontrollers that artificially mobilize the joints without anyinteraction from the amputee and are only capable of generating basicmotions. Such basic controllers do not take into consideration thedynamic conditions of the working environment, regardless the fact thatthe prosthesis is required to generate appropriate control within apractical application. They are generally lacking in predictive controlstrategies necessary to anticipate the artificial limb's response aswell as lacking in adaptive regulation enabling the adjustment of thecontrol parameters to the dynamics of the prosthesis. Because human limbmobility is a complex process including voluntary, reflex and randomevents at the same time, conventional prostheses do not have thecapability to interact simultaneously with the human body and theexternal environment in order to have minimal appropriate functioning.

Accordingly, it is an object of the present application to obviate ormitigate some or all of the above disadvantages.

SUMMARY

According to the present invention, there is provided an instrumentedprosthetic foot for use with an actuated leg prosthesis controlled by acontroller, the instrumented prosthetic foot comprising a connector toconnect the instrumented prosthetic foot to the leg prosthesis, an anklestructure connected to the connector, a ground engaging member connectedto the ankle, at least one sensor for detecting changes in weightdistribution along the foot, and an interface for transmitting signalsfrom the sensor to the controller.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments of the invention will be described by way of example onlywith reference to the accompanying drawings, in which:

FIG. 1 shows the lower body of an individual provided with a prosthesisand an instrumented prosthetic foot on one side and having a healthy legon the other side.

FIG. 2 is a block diagram showing a control system for a prosthesishaving an actuating mechanism.

FIG. 3 is a perspective view, from the front and slightly above, of ainstrumented prosthetic foot.

FIG. 4 is an exploded perspective view of the instrumented prostheticfoot of FIG. 3.

FIG. 5 is a perspective view, from the front and slightly above, of analternative embodiment of the instrumented prosthetic foot of FIG. 3.

FIG. 6 is an exploded perspective view of the instrumented prostheticfoot of FIG. 5.

FIG. 7 is a perspective view, from the front and slightly above, ofanother alternative embodiment of the instrumented prosthetic foot ofFIG. 3

FIG. 8 is an exploded perspective view of the instrumented prostheticfoot of FIG. 7.

FIG. 9 is schematic view of forces exerted on a foot.

FIG. 10 is a perspective view, from the front and slightly above, of afurther still alternative embodiment of the instrumented prosthetic footof FIG. 3.

FIG. 11 is an exploded perspective view of the instrumented prostheticfoot of FIG. 10.

FIG. 12 is a perspective view, from the front and slightly above, of ayet further still alternative embodiment of the instrumented prostheticfoot of FIG. 3.

FIG. 13 is an exploded perspective view of the instrumented prostheticfoot of FIG. 12.

FIG. 14 is a perspective view, from the front and slightly above, of afurther alternative embodiment of the instrumented prosthetic foot ofFIG. 3.

FIG. 15 is an exploded perspective view of the instrumented prostheticfoot of FIG. 14.

DETAILED DESCRIPTION

The appended figures show a instrumented prosthetic foot (20) havingsensors (22A, 22B) for use, in cooperation with possible additionalsensors (24A, 24B, 26), with a control system (100) for controlling aprosthesis (14) having an actuating mechanism (16). It should beunderstood that the present invention is not limited to the illustratedimplementation since various changes and modifications may be effectedherein without departing from the scope of the appended claims.

Referring therefore to FIG. 1 an individual (10) has a pair of legs (26)and (28), one of which, (26), is amputated above the knee. A prosthesis(14) is attached to the leg (26) and includes an actuating mechanism(16), which may be either passive or active. An instrumented prostheticfoot (20) is attached to the prosthesis (14) and includes sensors (22A,22B). Additional sensors (24A, 24B) are located on the healthy foot andadditional sensors (26) located on the individual (10) and/or theprosthesis (14). A passive actuating mechanism may be generally definedas an electromechanical component that only absorbs mechanical energy inorder to modify dynamics of mechanical joints of the prosthesis, whilean active actuating mechanism may be generally defined as anelectromechanical component that absorbs and supplies mechanical energyin order to set dynamics of mechanical joints of the prosthesis.

An example of a passive actuating mechanism is described in U.S. patentapplication Ser. No. 09/767,367, filed Jan. 22, 2001, entitled“ELECTRONICALLY CONTROLLED PROSTHETIC KNEE”. Examples of activeactuating mechanisms are described in U.S. patent application Ser. No.10/463,495 filed Jun. 17, 2003, entitled “ACTUATED PROSTHESIS FORABOVE-KNEE AMPUTEES”, by Stéphane Bédard et al., the entire disclosureof which is hereby incorporated by reference herein.

The prosthesis (14) is controlled, as shown schematically in FIG. 2, bya basic control system (100) comprising sensors (22A, 22B, 24A, 24B,26), connected through an interface (30) to a controller (40). Thecontroller (40) provides signals to an actuating mechanism (16) in theprosthesis (14), such as shown in FIG. 1. The purpose of the controlsystem (100) is to provide the required signals for controlling theactuating mechanism (16). To do so, the control system (100) isinterfaced with the amputee (10) using sensors (22A, 22B, 24A, 24B, 26)to ensure proper coordination between the amputee (10) and the movementsof the prosthesis (14). The sensors (22A, 22B, 24A, 24B, 26) captureinformation, in real time, about the dynamics of the amputee's movementand provide that information to the controller (40) via the interface(30). The controller (40) then uses the information to determine theresistance to be applied to a joint, in the case of a passive actuatingmechanism, or the joint trajectories and the required angular force ortorque that must be applied by a joint, in the case of an activeactuating mechanism, in order to provide coordinated movements.

The sensors (22A, 22B, 24A, 24B, 26) may include myoelectric sensors,neuro-sensors, kinematic sensors, kinetic sensors, strain gauges orplantar pressure sensors. Myoelectric sensors are electrodes used tomeasure the internal or the external myoelectrical activity of skeletalmuscles. Neuro-sensors are electrodes used to measure the summation ofone or more action potentials of peripheral nerves. Kinematic sensorsare used to measure the position of articulated joints, the mobilityspeed or acceleration of lower extremities. Kinetic sensors are used tomeasure angular forces at articulated joints or reaction forces of lowerextremities. Strain gages are used to measure the strain forces at aspecific underfoot area. Plantar pressure sensors are used to measurethe vertical plantar pressure of a specific underfoot area. Of course,additional types of sensors which provide various information aboutdynamics of human locomotion may be used. For a given application, theuse of sensors (22A, 22B, 24A, 24B, 26) is not restricted to a specifictype of sensor, multiple types of sensors in various combinations may beused.

As illustrated in FIG. 1, the sensors (22A, 22B,) may comprise localizedplantar pressure sensors located at spaced locations on the prostheticfoot (20) to measure the vertical plantar pressure of a specificunderfoot area. Similarly, the plantar pressure sensors (24A, 24B)located on the side of the healthy foot may be provided at spacedlocations in a custom-made insole, preferably in the form of a standardorthopaedic insole, that is modified to embed the two sensors (24A, 24B)for the measurement of two localized plantar pressures. The sensors(22A, 22B, 24A, 24B) are operable to measure the weight transfer alongthe foot as the individual moves which may be combined with othersensors (26) such as kinematic sensors to measure the angular speed ofbody segments of the lower extremities and kinematic sensors to measurethe angle of the prosthesis (14) knee joint.

Each sensor (22A, 22B, 24A, 24B) may comprise a thin Force-SensingResistor (FSR) polymer cell directly connected to the interface (30) ofthe control system (100) or indirectly using an intermediary system (notshown), for instance a wireless emitter. Of course, other types ofcommunication link technologies may be used, such as, for example,optical. The FSR cell has a decreasing electrical resistance in responseto an increasing force applied perpendicularly to the surface thereof.Each cell outputs a time variable electrical signal for which theintensity is proportional to the total vertical plantar pressure overits surface area. The size and position of the plantar pressure sensors(22A, 22B, 24A, 24B) may be defined in accordance with the stability andthe richness (intensity) of the localized plantar pressure signalsprovided by certain underfoot areas during locomotion. For example, itwas found by experimentation that the heel and the toe regions are tworegions of the foot sole where the Plantar Pressure Maximum Variation(PPMV) may be considered as providing a signal that is both stable andrich in information.

Accordingly, the controller (40) may use the data signals from the fourlocalized plantar pressure sensors (22A, 22B, 24A, 24B), as well as theinformation gathered from the data signals of the other sensors (26)such as kinematic sensors, in order to decompose the locomotion of theindividual (10) into a finite number of states, and generate theappropriate control signals for controlling the actuating mechanism (16)according to the locomotion. Of course, the controller (40) is notlimited to the use of the preceding data signals.

An example of a controller (40) and control system (100) using sensorscomprising plantar pressure sensors as well as kinematic sensors isdescribed in U.S. patent application Ser. No. 10/600,725 filed Jun. 20,2003, entitled “CONTROL SYSTEM AND METHOD FOR CONTROLLING AN ACTUATEDPROSTHESIS”, by Stéphane Bédard, the entire disclosure of which ishereby incorporated by reference herein.

To facilitate the acquisition of the data in a repeatable and dependablemanner, the sensors (22A, 22B) are incorporated in to the structure ofthe foot (20). An embodiment of the instrumented prosthetic foot (20) isshown in more detail in FIGS. 3 and 4. The instrumented prosthetic foot(20) includes a foot plate (53), forming an elongated body, with aconnector (51) at one end, a toe plate (55A) and a heel plate (55B) thatis cantilevered from the foot plate (53). Such an arrangement isprovided by, for example, a Vari-Flex® prosthetic foot from Össur.Pressure sensors (22A, 22B) are located at longitudinally spacedlocations on the underside of the foot plate (53) and heel plate (55)respectively. The sensors (22A, 22B) are covered by rigid plates (52A,52B) and resilient pads (54A, 54B). The pressure sensors (22A, 22B) arelocated so as to be responsive to loads imposed on the instrumentedprosthetic foot (20) at the regions corresponding to the toe area andthe heel area respectively.

The rigid plates (52A, 52B) covering the sensors (22A, 22B), althoughnot essential, help to optimize the pressure distribution on the entiresurface of the sensors (22A, 22B) as well as inhibiting any shearing andmay be made of 85A durometer polyurethane. Of course, other type ofmaterial may be used as well.

The pads (54A, 54B) wrap up the rigid plates (52A, 52B) and the sensors(22A, 22B), forming a ground engaging member, in order to optimize thecontact between the instrumented prosthetic foot (20) and the ground.The pads (54A, 54B) may be made of 40A durometer polyurethane. Ofcourse, other type of material may be used as well.

In operation, therefore, as the foot (20) traverses the ground, theforce applied to the heel plate (55B) is measured by the sensor (22B)and a corresponding signal forwarded to the controller (40). The forceapplied to the toe plate (55A) is also measured by the sensor (22A) andthe relative loading between the two locations is measured. As the foot(20) continues to traverse the ground, the force applied to the toe areaincreases and that at the heel decreases to provide a pair of signalsfrom which the disposition of the leg may be determined and theappropriate control provided to the actuator (16).

An alternative embodiment of the instrumented prosthetic foot (20) isshown in FIGS. 5 and 6. The instrumented prosthetic foot (20) includesconnector (61), foot plate (63), toe plate (64A) and heel plate (64B),such as provided by, for example, a Vari-Flex® prosthetic foot fromÖssur. Pressure sensors (22A, 22B) are located between the foot plate(63) and rigid plates (62A, 62B). The pressure sensors (22A, 22B) arelocated so as to be responsive to load imposed on the instrumentedprosthetic foot (20) at the regions corresponding to the toe area andthe heel area respectively. More specifically, pressure sensor (22A) issandwiched between a pair of rigid plates (62A), which in turn arepositioned between the heel plate (64B) and the foot plate (63).Pressure sensor (22B) is sandwiched between a pair of rigid plates(62B), which in turn are positioned between the foot plate (63) and theconnector (61).

As for the previous embodiment, rigid plates (62A, 62B) covering thesensors (22A, 22B), although not essential, help to optimize thepressure distribution on the entire surface of the sensors (22A, 22B) aswell as inhibiting any shearing and may be made of 85A durometerpolyurethane. Of course, other type of material may be used as well.

Another alternative embodiment of the instrumented prosthetic foot (20)is shown in FIGS. 7 and 8. The instrumented prosthetic foot (20)includes connector (71), top foot plate (75), foam cushion core (73) andbottom foot plate (74), such as provided by, for example, a LP Talux®prosthetic foot from Össur. Pressure sensors (22A, 22B) are sandwichedbetween pairs of rigid plates (72A, 72B). The pressure sensors (22A,22B) are located so as to be responsive to load imposed on theinstrumented prosthetic foot (20) at the regions corresponding to thetoe area and the heel area respectively. More specifically, pressuresensor (22A) is sandwiched between a pair of rigid plates (72A), whichin turn are positioned within gap (76A), which is located between abottom foot plate (74) and a foam cushion core (73). Pressure sensor(22B) is sandwiched between a pair of rigid plates (72B), which in turnare positioned within gap (76B), which is located within the foamcushion core (73).

Again, as for the previous embodiments, rigid plates (72A, 72B) coveringthe sensors (22A, 22B), although not essential, help to optimize thepressure distribution on the entire surface of the sensors (22A, 22B) aswell as preventing any shearing and may be made of 85A durometerpolyurethane. Of course, other type of material may be used as well.

In the previous embodiments, the force (or pressure) at the toe and heelareas, F_toe and F_heel respectively, was obtained by positioningpressure sensors (22A, 22B) directly at those areas. More specifically,referring to FIG. 9, F_toe and F_heel were obtained as follows:F_toe=F_toe_meas  Equation 1F_heel=F_heel_meas  Equation 2

In other possible embodiments of the instrumented prosthetic foot (20),sensors (22A, 22B) may not be restricted to being positioned directly atthe toe and heel areas, the equivalent information may be obtained bymeasuring the equivalent torque at the ankle and the axial force at theconnector of the instrumented prosthetic foot (20). F_toe and F_heel maybe defined in terms of the torque measured at the ankle, M_ankle_meas,and the force measured at the connector, F_conn_meas, using thefollowing equations: $\begin{matrix}{{F\_ toe} = \frac{{{M\_ ankle}{\_ meas}} + \left( {{F\_ conn}{{\_ meas} \cdot {l\_ heel}}} \right)}{\left( {{l\_ heel} + {l\_ toe}} \right)}} & {{Equation}\quad 3} \\{{F\_ heel} = \frac{{{- {M\_ ankle}}{\_ meas}} + \left( {{F\_ conn}{{\_ meas} \cdot {l\_ toe}}} \right)}{\left( {{l\_ heel} + {l\_ toe}} \right)}} & {{Equation}\quad 4}\end{matrix}$

-   -   where    -   I_heel is the distance between the center of the connector and        the center of the heel area;    -   I_toe is the distance between the center of the connector and        the center of the toe area.

Following the previous discussion about the locations of sensors (22A,22B), a further alternative embodiment of the instrumented prostheticfoot (20) is shown in FIGS. 10 and 11. The instrumented prosthetic foot(20) includes connector (81), foot plate (83), toe plate (84A) and heelplate (84B), such as provided by, for example, a Vari-Flex® prostheticfoot from Össur, and load cells (22A, 22B). Load cells (22A, 22B) arelocated below connector (91), load cell (22A) being slightly biasedtowards the toe area of the foot and load cell (22B) being slightlybiased towards the heel area. Since the sensors (22A, 22B) are notlocated directly at the toe and heel areas, Equation 3 and Equation 4may be used, for example by controller (40), to compute the equivalentpressures at the toe and heel areas by defining the equivalent torque atthe ankle and the axial force at connector (81) as follows:F _(—) conn _(—) meas=F_22 B+F_22 A  Equation 5M _(—) ankle _(—) meas=F _(—22) B·I_22 B−F_22 A·I_22 A  Equation 6

-   -   where    -   F_22B is the force measured at sensor 22B;    -   F_22A is the force measured at sensor 22A;    -   I_22B is the distance between the center of the connector (81)        and the center of sensor 22B;    -   I_22A is the distance between the center of the connector (81)        and the center of sensor 22A.

In the previous embodiments of the instrumented prosthetic foot (20),the force (or pressure) at the toe and heel areas, F_toe and F_heelrespectively, was obtained either by positioning pressure sensors (22A,22B) directly at those areas or by positioning pressure sensors or loadcells (22A, 22B) in other areas and obtaining the equivalent informationby computing the equivalent torque at the ankle and the axial force atthe connector. Other types of sensors may also be used to obtain theequivalent torque at the ankle and the axial force at the connector.Such an example is illustrated by a further still embodiment of theinstrumented prosthetic foot (20), which is shown in FIGS. 12 and 13.The instrumented prosthetic foot (20) includes connector (91), mountedon pivoting ankle (93). Bumpers (92A, 92B) are positioned between thepivoting ankle (93) and rocker plate (95) located on a foot plate (94).

The pivoting ankle (93) is connected to the rocker plate (95) by a pivotpin (96). Such an arrangement is provided by, for example, an Elation®prosthetic foot from Össur.

A load cell (22A) and an optical encoder (22B). are incorporated intothe foot (20) to provide measurement of the distribution of forces alongthe foot (20). Load cell (22A) is positioned between connector (91) andpivoting ankle (93). Optical encoder (22B) comprises reader (221) anddisk (223). Reader (221) is located on pivoting ankle (93) while disk(223) is located on rocker plate (95) and encircles pivot pin (96). Onceagain, Equation 3 and Equation 4 may be used, for example by controller(40), to compute the equivalent pressures at the toe and heel areas bydefining the equivalent torque at the ankle and the axial force atconnector (91) as follows:F_conn_meas=F_22A  Equation 7M _(—) ankle _(—) meas=R _(—) ankle _(—) meas·R _(—) const  Equation 8

-   -   where    -   F_22A is the force measured at sensor 22A;    -   R_ankle_meas is the rotation measurement of pivoting ankle (93)        about pivot pin (96) as measured by optical encoder (22B);    -   R_const is a constant associated with the resistance of bumpers        (92A, 92B) to compression, which constant varies depending in        the material used.

A yet further alternative embodiment of the instrumented prosthetic foot(20) is shown in FIGS. 14 and 15. The instrumented prosthetic foot (20)includes connector (101), mounted on pivoting ankle (103). Bumpers(102A, 102B) are positioned between the pivoting ankle (103) and rockerplate (105) located on a foot plate (104). The pivoting ankle (103) isconnected to the rocker plate (105) by a pivot pin (106). Such anarrangement is provided by, for example, an Elation® prosthetic footfrom Össur. Pressure sensors (22A, 22B) and load cell (22C) areincorporated into the foot (20) to provide measurement of thedistribution of forces along the foot (20). Pressure sensor (22A) ispositioned between rocker plate (85) and bumper (82A) while pressuresensor (22B) is positioned between rocker plate (85) and bumper (82B). Aload cell (22C) is positioned between connector (91) and pivoting ankle(93).

In this embodiment, Equation 6 is used to compute the equivalent torqueat the ankle, while the axial force at connector (101) is computed usingthe following equation:F_conn_meas ═F_22C  Equation 9

Load cell (22C) is required to compute the axial force at connector(101) since when there is no torque at the ankle, i.e. the wearer of theprosthesis is standing still, the axial force is being exerted in itsentirety onto pivot pin (96).

In all of the described embodiments, the sensors (22A, 22B) may bedirectly connected to interface (30) of control system (100) orindirectly using an intermediary system (not shown), for instance awireless emitter. Of course, other types of communication linktechnologies may be used, such as, for example, optical.

Other types of non-articulated or articulated prosthetic foot may beused as well as long as the selected prosthetic foot providesapproximately the same dynamical response as the ones mentioned hereabove. Nevertheless, an articulated foot offers the best performances.The instrumented prosthetic foot (20) may further have an exposed metalor composite structure or it may have a cosmetic covering that gives itthe appearance of a human ankle and foot.

It should be noted that the present invention is not limited to its usewith the mechanical configuration illustrated in FIG. 1 or the controlsystem (100) illustrated in FIG. 2. It may be used with a leg prosthesishaving more than one joint. For instance, it may be used with aprosthesis having an ankle joint, a metatarsophalangeal joint or a hipjoint in addition to a knee joint. Moreover, instead of a conventionalsocket a osseo-integrated devices could also be used, ensuring a directattachment between the mechanical component of the prosthesis and theamputee skeleton. Other kinds of prostheses may be used as well.

1. An instrumented prosthetic foot for use with an actuated legprosthesis controlled by a controller, the instrumented prosthetic footcomprising: an elongated body having a top and a bottom part; aconnector to connect the instrumented prosthetic foot to the legprosthesis, the connector being attached to the top part of theelongated body; a ground engaging member attached to the bottom part ofthe elongated body; at least one sensor for detecting changes in weightdistribution along the foot; and an interface for transmitting signalsfrom the sensor to the controller.
 2. An instrumented prosthetic footaccording to claim 1, wherein: the ground engaging member includes apair of basic underfoot locations, the first region corresponding to theheel area of the human foot and second region corresponding to the toearea of the human foot.
 3. An instrumented prosthetic foot according toclaim 2, wherein: at least two sensors are provided, one of the sensorsbeing associated with each basic underfoot locations of the groundengaging member.
 4. An instrumented prosthetic foot according to claim3, wherein: the sensors include a strain sensor to measure the strainapplied at a corresponding basic underfoot location of the groundengaging member.
 5. An instrumented prosthetic foot according to claim3, wherein: the sensors include a pressure sensor to measure thepressure applied at a corresponding basic underfoot location of theground engaging member.
 6. An instrumented prosthetic foot according toclaim 3, wherein: the sensors include a load cell to measure thepressure applied at a corresponding basic underfoot location of theground engaging member.
 7. An instrumented prosthetic foot according toclaim 3, wherein: the sensors are positioned under the ground engagingmember.
 8. An instrumented prosthetic foot according to claim 3,wherein: the sensors are positioned between the ground engaging memberand the elongated body.
 9. An instrumented prosthetic foot according toclaim 3, wherein: the sensors are positioned between the elongated bodyand the connector.
 10. An instrumented prosthetic foot according toclaim 5, wherein: the pressure sensor is a force-sensing resistor. 11.An instrumented prosthetic foot according to claim 5, furthercomprising: a rigid plate placed on at least one side of the sensor. 12.An instrumented prosthetic foot according to claim 11, furthercomprising: a resilient pad covering the rigid plate and the sensor. 13.An instrumented prosthetic foot according to claim 1, furthercomprising: an ankle structure pivotally connecting the elongated bodyto the connector.
 14. An instrumented prosthetic foot according to claim13, wherein: at least two sensors are provided, the sensors includingtwo load cells positioned between the connector and the ankle structure.15. An instrumented prosthetic foot according to claim 13, wherein: atleast two sensors are provided, the sensors including an optical encoderand a load cell, the optical encoder being positioned on the anklestructure about its pivot axis with the elongated body and the load cellbeing positioned between the ankle structure and the connector.
 16. Aninstrumented prosthetic foot according to claim 1, wherein: theinterface for transmitting signals from the sensor to the controller isa wired connection.
 17. An instrumented prosthetic foot according toclaim 1, wherein: the interface for transmitting signals from the sensorto the controller is a wireless connection.
 18. An instrumentedprosthetic foot according to claim 1, further comprising: means forremovably connecting the instrumented prosthetic foot to the legprosthesis.